Has a World Baseball Classic game ever ended 18-2?
Exactly once. On March 3, 2006, Japan beat China 18-2, and no World Baseball Classic game before or since has ended that way. When it happened it was a scorigami, the first 18-2 in league history.
That makes 18-2 the 47th most common final score out of 80 that have ever occurred in World Baseball Classic. One point away, 19-2 has happened never and 18-3 has happened never.